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.TH PTHREAD_SIGMASK 3 2021-03-22 "Linux" "Linux Programmer's Manual"
.SH NAME
pthread_sigmask \- examine and change mask of blocked signals
.SH SYNOPSIS
.nf
.B #include <signal.h>
.PP
.BI "int pthread_sigmask(int " how ", const sigset_t *" set \
", sigset_t *" oldset );
.fi
.PP
Compile and link with \fI\-pthread\fP.
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR pthread_sigmask ():
.nf
    _POSIX_C_SOURCE >= 199506L || _XOPEN_SOURCE >= 500
.fi
.SH DESCRIPTION
The
.BR pthread_sigmask ()
function is just like
.BR sigprocmask (2),
with the difference that its use in multithreaded programs
is explicitly specified by POSIX.1.
Other differences are noted in this page.
.PP
For a description of the arguments and operation of this function, see
.BR sigprocmask (2).
.SH RETURN VALUE
On success,
.BR pthread_sigmask ()
returns 0;
on error, it returns an error number.
.SH ERRORS
See
.BR sigprocmask (2).
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR pthread_sigmask ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
.SH CONFORMING TO
POSIX.1-2001, POSIX.1-2008.
.SH NOTES
A new thread inherits a copy of its creator's signal mask.
.PP
The glibc
.BR pthread_sigmask ()
function silently ignores attempts to block the two real-time signals that
are used internally by the NPTL threading implementation.
See
.BR nptl (7)
for details.
.SH EXAMPLES
The program below blocks some signals in the main thread,
and then creates a dedicated thread to fetch those signals via
.BR sigwait (3).
The following shell session demonstrates its use:
.PP
.in +4n
.EX
.RB "$" " ./a.out &"
[1] 5423
.RB "$" " kill \-QUIT %1"
Signal handling thread got signal 3
.RB "$" " kill \-USR1 %1"
Signal handling thread got signal 10
.RB "$" " kill \-TERM %1"
[1]+  Terminated              ./a.out
.EE
.in
.SS Program source
\&
.EX
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <errno.h>

/* Simple error handling functions */

#define handle_error_en(en, msg) \e
        do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)

static void *
sig_thread(void *arg)
{
    sigset_t *set = arg;
    int s, sig;

    for (;;) {
        s = sigwait(set, &sig);
        if (s != 0)
            handle_error_en(s, "sigwait");
        printf("Signal handling thread got signal %d\en", sig);
    }
}

int
main(int argc, char *argv[])
{
    pthread_t thread;
    sigset_t set;
    int s;

    /* Block SIGQUIT and SIGUSR1; other threads created by main()
       will inherit a copy of the signal mask. */

    sigemptyset(&set);
    sigaddset(&set, SIGQUIT);
    sigaddset(&set, SIGUSR1);
    s = pthread_sigmask(SIG_BLOCK, &set, NULL);
    if (s != 0)
        handle_error_en(s, "pthread_sigmask");

    s = pthread_create(&thread, NULL, &sig_thread, &set);
    if (s != 0)
        handle_error_en(s, "pthread_create");

    /* Main thread carries on to create other threads and/or do
       other work. */

    pause();            /* Dummy pause so we can test program */
}
.EE
.SH SEE ALSO
.BR sigaction (2),
.BR sigpending (2),
.BR sigprocmask (2),
.BR pthread_attr_setsigmask_np (3),
.BR pthread_create (3),
.BR pthread_kill (3),
.BR sigsetops (3),
.BR pthreads (7),
.BR signal (7)
.SH COLOPHON
This page is part of release 5.13 of the Linux
.I man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
\%https://www.kernel.org/doc/man\-pages/.
